Watch out, solar manufacturers: GE may be about to take over your turf. The corporate giant, which has already carved out a spot as one of the world's leading wind turbine suppliers, announced this week that it is moving into the thin film solar business.

Nanosolar, a Silicon Valley thin-film solar startup, has been ridiculed for its reluctance to release any sort of information about its technology since it debuted in 2002. And now the company has proved all its detractors wrong, announcing yesterday that it has $4.1 billion in orders for its relatively cheap thin-film photovoltaic solar panels.

Nevada is a veritable gold mine of solar energy, so it's not surprising to hear that photovoltaic company First Solar is teaming up with Sempra Generation to build the largest solar photovoltaic plant in the U.S. in Boulder City, Nevada, about 40 miles south of Las Vegas.

You have seen our Fast Company 50. But what are the companies within specific categories doing creative and ground-breaking work? Who is leading an industry into the future? Here we present the top ten firms in Clean Energy.